Santonox, 4,4'-thio-bis(6-tert-butyl-m-cresol), has been recommended for study in the NTP as a representative of the class of rubber antioxidants which have widespread industrial usage and a high potential for occupational exposure. Santonox is relatively non-toxic, with an oral LD50 of approximately 5g/kg. Before being tested in the bioassay program, disposition studies are needed to assess its absorption, distribution, metabolism, and excretion. Santonox causes severe gastroenteritis after oral exposure. After iv administration, the compound was rapidly conjugated with glucuronicucid in the liver and excreted via the bile into the feces. About 10% of the doses persists in the liver, skin and adipose tissue, suggesting the possibility of accumulation upon chronic exposure.